Hi,
Here’s a link to the [https://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-15-3543-laptop_service%20manual_en-us.pdf|service manual] for the laptop, taken from this [https://www.dell.com/support/home/us/en/04/product-support/product/inspiron-15-3543-laptop/manuals|webpage].
Scroll to p.75 to view the necessary pre-requisite steps and then the procedure to remove/replace the heat sink assembly. The fan is part of the assembly.
Search online for ''Inspiron 3543 fan'' or ''9W0J6'' (this is the part number) to get results for suppliers of the part.